The invention applies most particularly to underwater vehicles comprising a vectored thruster with two propellers. A thruster is said to be a vectored thruster when it is able to be controlled in such a way as to produce a thrust or propulsive force that is able to be oriented over 4π steradians. What is termed vectored propulsion of an underwater vehicle is in opposition to conventional propulsion, in which the orientation of fins brings about a modification in the lift generated by the flow of fluid surrounding the fins. The force generated by the fluid on the fins allows the vehicle to be oriented in the desired direction. One well-known limit of this form of propulsion is the requirement to generate a significant flow of fluid around the vehicle in order to bring about a change in lift of the fins that allows the attitude of the vehicle to be changed, that is to say in order to allow the underwater vehicle to be maneuvered. If this flow is too weak, then the effectiveness of the fins drops inversely with the square of the speed of the flow, until it becomes zero for a zero flow speed. In other words, it is not possible using conventional propulsion to orient the vehicle in a desired direction without significant displacement of the vehicle when the flow of fluid is zero. Moreover, the fins generate a drag proportional to the square of the speed that opposes the displacement and that therefore consumes energy, the more so the more the fins are invoked. The method for controlling vectored propulsion presented in the present patent allows the vehicle to dispense with conventional directional fins, and therefore to significantly reduce the hydrodynamic drag of the vehicle. Vectored propulsion of the type with two propellers exhibits numerous theoretical advantages, in particular increased mobility, simplification of the architecture (e.g. by eliminating the fins), and an increase in the endurance of the vehicle (by reducing the hydrodynamic drag). This absence of fins other than the blades of the propellers facilitates the implementation of what is termed a “flush” hydrodynamic vehicle, that is to say from which no appendage protrudes, thereby allowing it for example to fit easily in a tube and avoiding damaging the fins when berthing.
However, controlling this type of thruster encounters numerous difficulties, in particular when turning.